The present invention relates to a method of making pattern data to be stored in a sewing machine for controlling the needle positions and the feeding amounts as well as the directions thereof to thereby provide a selected pattern of stitches.
With respect to sewing machines which use conventional mechanical cams, the number of stitches to be used per pattern is at most 20. It has therefore been sufficient to provide the pattern data on a cam in accordance with a designed pattern in such a manner that the designed pattern may be produced with the stitches continued from the first to the last. For example, the last stitch may be returned accurately to the first stitch of the pattern, because there is not so much accumulated error of the fabric feeding due to the comparatively small number of total stitches.
Recently computer sewing machines have been developed. Such sewing machines electronically store the pattern data for controlling the needle positions and feeding amounts as well as the directions thereof. Moreover the number of different types of pattern data that can be stored is limitless, and accordingly complicated patterns may be produced with many stitches. However, it has often been inconvenient with the conventional method of making the pattern data.
Namely in the case when the patterns are formed from stitches, which include two or more stitches to be required to come to one point or come into alignment after many intervening stitches have been formed between the two stitches, no problem arises in the needle amplitude direction, but a problem arises in the fabric feeding direction. More precisely, two stitches, i.e. a precedingly formed stitch and a later formed stitch will often fail to come to one point or come into alignment due to the accumulated error of feeding pitches intervening between the two stitches, is dependent upon the kind or thickness of fabric to be sewn. As the result, the stitched pattern becomes considerably deformed.